Heretofore, a photographic process using silver halide has most widely been practiced, since it provides excellent sensitivity, gradation, and like photographic properties as compared with, for example, an electrophotographic process and a diazo type photographic process. In recent years, techniques have been developed which provide images easily in a short time by employing, as photographic processing of forming images on light-sensitive materials using silver halide, a dry processing involving heating in place of the conventional wet processing involving development in a developing solution.
Thermally developable light-sensitive materials are known in the art, and the thermally developable light-sensitive materials and the process thereof are described in, for example, "Shashin Kagaku no Kiso", pp. 553-555 (published by Corona Co., Ltd.), "Elizo Joho", Apr. 1978, p. 40, "Nebletts Handbook of Photography and Reprography", 7th Ed. (Van Norstrand Reinhold Company), pp. 32-33, U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, 3,457,075, British Pat. Nos. 1,131,108, 1,167,777, and Research Disclosure, June, 1978, pp. 9-15 (RD-17029).
Many processes have been proposed for obtaining color images. As to a process of forming color images by binding an oxidation product of a developing agent with a coupler, U.S. Pat. No. 3,531,286 proposes p-phenylenediamine type reducing agents and phenolic or active methylene couplers, U.S. Pat. No. 3,761,270 proposes p-aminophenol type reducing agents, Belgian Pat. No. 802,519 and Research Disclosure, the September issue of 1975, pp. 31 and 32 propose sulfonamidophenol type reducing agents, and U.S. Pat. No. 4,021,240 proposes a combination of sulfonamidophenol type reducing agents and 4-equivalent couplers.
As to the process of forming positive color images by a light-sensitive silver-dye bleach process, useful dyes and bleaching processes are described in, for example, Research Disclosure, the April issue of 1976, pp. 30-32 (RD-14433), ibid., the December issue of 1976, pp. 14-15 (RD-15227), U.S. Pat. No. 4,235,957, etc.
Further, an image-forming process by thermal development utilizing compounds which possess a previously formed dye moiety and which can release a mobile dye as a direct or inverse function of the reduction reaction of silver halide to silver at elevated temperatures is disclosed in European Patent Laid-Open Nos. 76,492 and 79,056, and Japanese Patent Application (OPI) Nos. 28,928/83 and 26, 008/83 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application").
In addition, U.S. Pat. Nos. 4,500,626, 4,483,914, U.S. patent application Ser. No. 509,592 (filed on March 16, 1984), etc. describe the process of transferring a mobile dye imagewise formed by thermal development to an image-receiving layer by heating, and the image-receiving materials for the process. On the other hand, however, since the necessary photographic reagents are not expected to be fed from a developing solution or the like, all the photographic reagents necessary for development must be incorporated in advance in the light-sensitive materials. However, if such photographic reagents are added to the photographic light-sensitive materials in an active form, they will react with the other ingredients in the photographic light-sensitive materials during storage before being processed or will be decomposed by the influence of heat, oxygen, or the like, thus being unable to exhibit the expected capabilities upon processing. As one technique for solving this problem, there is a technique of blocking the active group of a photographic reagent to add it in a substantially inert form, i.e., as a photographic reagent precursor, to a photographic light-sensitive material. Where the useful photographic reagent is a dye, a functional group exerting a great influence on spectral absorption of the dye is blocked to shift the spectral absorption of dye to a shorter wavelength side or a longer wavelength side. This technique provides an advantage that, even when the dye is incorporated in the silver halide emulsion layer having the same light-sensitive spectral region, reduction in sensitivity due to the so-called filter effect never takes place. Where the useful photographic reagent is an anti-foggant or a development inhibitor, blocking of the active group thereof provides such advantages as that the desensitization effect due to adsorption thereof onto light-sensitive silver halide or formation of silver salts during storage, can be depressed and, at the same time that fog is reduced, excess development is depressed, or development is stopped at a necessary point, by the timely release of the photographic reagents. Where the useful photographic reagent is a developing agent, an auxiliary developing agent or a fogging agent, blocking of the active group or adsorptive group thereof provides such advantages as that various photographic adverse influences due to formation of semiquinones or oxidation products by air oxidation during storage are prevented, or that formation of fogging nuclei during storage is prevented by preventing the electron injection into the silver halide, thus realizing a stable processing. Where the photographic reagent is a bleaching accelerator or a bleach-fixing accelerator, blocking of the active group thereof provides the advantage that the reaction thereof with the other ingredients incorporated in the photogarphic light-sensitive materials is depressed during storage and, upon processing, the desired properties appear timely by removing the blocking group.
As to such blocking techniques for photographic reagents, several specific techniques have already been known with respect to the conventional photographic light-sensitive materials. For example, it has been known to utilize such blocking agents as an acyl group, a sulfonyl group, etc. described in Japanese Patent Publication No. 44,805/72; to utilize those blocking groups described in Japanese patent Publication Nos. 17,369/79, 9,696/80, and 34,927/80 and which release the photographic reagents by so-called reverse Michael reaction; to utilize those blocking groups described in Japanese Patent Publication No. 39,727/79, Japanese Patent Application (OPI) Nos. 135,944/82, 135,945/82, and 136,640/82 which release the phtotgraphic reagents upon formation of quinonemethide or quinonemethide-like compounds by intramolecular electron transfer; to utilize the intramolecular ring-closing reaction described in Japanese Patent Application No. 53,330/80; or to utilize 5- or 6-membered ring cleavage described in Japanese Patent Application (OPI) Nos. 76,541/82, 135,949,82, and 179,842/82. However, all of these known techniques utilize hydrolysis or deprotonation by the action of OH.sup.- upon wet-process development, and no precursor techniques for dry processing using an organic base have been known.